Event-Related Potential Evidence of Enhanced Visual Processing in Auditory-Associated Cortex in Adults with Hearing Loss.

OBJECTIVE: The present study investigated the characteristics of visual processing in the auditory-associated cortex in adults with hearing loss using event-related potentials. METHODS: Ten subjects with bilateral postlingual hearing loss were recruited. Ten age- and sex-matched normal-hearing subjects were included as controls. Visual ("sound" and "non-sound" photos)-evoked potentials were performed. The P170 response in the occipital area as well as N1 and N2 responses in FC3 and FC4 were analyzed. RESULTS: Adults with hearing loss had higher P170 amplitudes, significantly higher N2 amplitudes, and shorter N2 latency in response to "sound" and "non-sound" photo stimuli at both FC3 and FC4, with the exception of the N2 amplitude which responded to "sound" photo stimuli at FC3. Further topographic mapping analysis revealed that patients had a large difference in response to "sound" and "non-sound" photos in the right frontotemporal area, starting from approximately 200 to 400 ms. Localization of source showed the difference to be located in the middle frontal gyrus region (BA10) at around 266 ms. CONCLUSIONS: The significantly stronger responses to visual stimuli indicate enhanced visual processing in the auditory-associated cortex in adults with hearing loss, which may be attributed to cortical visual reorganization involving the right frontotemporal cortex.